Just as 才 can express lateness, 就 (jiù) can be used to indicate that something happened earlier than expected.
Structure
The pattern is as follows:
subject+time+就+verb+object
In English this might be expressed with "as early as", but usually it's not specifically marked.
Examples
Tā shí bā suì jiù dà xué bì yè le.
她 十八 岁 就 大学 毕业 了。
她 十八 岁 就 大学 毕业 了。
She graduated from college when she was only 18 years old.
From the example sentences it is clear that 了 naturally occurs with a verb used after 就. This is because verbs following 就 generally have the feeling of being completed.
